ELECTRICITY: ELECTRICAL FIELDS #4

Field Basics

Scientists understood why forces acted the way they did when objects touched. The idea that confused them was forces that acted at a distance without touching. 
Think of examples such as gravitational force, electric force, and magnetic force. To help them explain what was happening, they used the idea of "field". They imagined that there was an area around the object, and anything that entered would feel a force. We say, for example, that the Moon has a gravitational field around it, and if you get close to the Moon, it will pull you down to its surface.

Electric Fields
An electric field describes the funky area near any electrically-charged object. Scientists don’t use the word "funky", but it works. It could also be called an electrostatic field. Any other charge that enters that area will feel a force, and the original object will also feel that force (Newton's Third Law). It's kind of like a spider sitting at the center of a web.

A normal field is a vector, and is represented by arrows. The Earth's (or any planet's) gravitational field would be drawn as arrows pointing toward the ground. A field vector shows the direction of the effect on an object entering the field. Gravity acts downward.

For an electric field, things are a little more complicated, since there are two kinds of charges, and some combinations attract while others repel. In order to be in agreement with each other, physicists decided that they would always use positive charges to determine the direction of the effect of a field. So, if the central charge was positive, and you put another positive charge near it, that second charge would be repelled outward. So the field vectors for a central positive charge point outward. If the central charge is negative, a positive charge placed nearby would be attracted toward the center charge, so the field vectors for a central negative charge point inward.

Since fields are directly related to the forces they exert, their strength decreases with distance, and increases with the size of the charge producing the field. When you put charges near one another, their fields interact and change shape. This results in changes in the PE of the objects, and generates forces of repulsion or attraction.

Electric fields can also be created by magnetic fields. Magnetism and electricity are always connected. 

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• ELECTRICAL CHARGES & CURRENTS, CHAPTER 12

ELECTRICITY: CONDUCTORS & CONDUCTIVITY #3

Conductors and Conductivity

There are many materials that allow charges to move easily. They are called conductors. Conductors have the quality of conductivity. I guess that's not a lot of help for you. The reality is that you just need to understand the difference between those two words. The conductor is the object that allows charge to flow. Conductivity is a quality related to the conductor. A material that is a good conductor gives very little resistance to the flow of charge. This flow of charge is called an electric current. A good conductor has high conductivity.

Different Types of ELECTRICAL Conductors

Electrical conductors are materials that allow electricity to flow through them easily. Most metals are good conductors.

Electrical insulators are materials that do not allow electricity to flow through them. Most plastic and ceramic materials are insulators.

In the diagram of an electrical insulator, the insulating material (plastic) surrounds the conducting material (copper wires).

(1) Metals are traditional conducting materials. You see them around the house all of the time. It's a metal wire or one of the metal prongs in an electric plug. There are a lot of free electrons in metallic conductors. Free electrons are electrons that are not being held in atoms, and so, can move easily. 

• Some of the best metallic conductors are copper (Cu), silver (Ag), and gold (Au). 

(2) There are some conductors that are not metals. Carbon is the best example.

(3) You've probably seen ionic conductors in a lab or in an experiment. When you think about ionic conductors, think about solutions and molten conductors. 

• A solution such as saltwater has a lot of free ions floating around. Those ions (charged atoms) can flow easily, and ionic solutions are very good conductors. 
• One of the reasons you need to get out of the water if there is lightning around, is that water normally contains dissolved ions, and if lightning hits the liquid (solution), it might conduct electricity long distances and electrocute you. 

(4) Semi-conductors are the conductors that make your computer possible. If it weren't for semi-conductors, most electronic doodads couldn't be made. Semiconductors have free electrons, but not as many as conductors, and they are not as easy to get moving. Semiconductors have low conductivities. 

• SEMI CONDUCTORS have both conducting and insulating properties and they are used to make electronic components. The way in which a semi-conducting material is connected to a power supply determines whether it will conduct an electrical current or prevent it from flowing.
• Examples are elements like silicon (Si) and germanium (Ge). 

Conductors and Insulators

Conductors are made of materials that electricity can flow through easily.
These materials are made up of atoms whose electrons can move away freely.

Some examples of conductors are: Copper Aluminum Platinum Gold Silver Water People and Animals Trees

Insulators are materials opposite of conductors. The atoms are not easily freed and are stable, preventing or blocking the flow of electricity.

Some examples of insulators are:

• Glass
• Porcelain
• Plastic
• Rubber

Electricity will always take the shortest path to the ground. Your body is 60% water and that makes you a good conductor of electricity. If a power line has fallen on a tree and you touch the tree you become the path or conductor to the ground and could get electrocuted.

The rubber or plastic on an electrical cord provides an insulator for the wires. By covering the wires, the electricity cannot go through the rubber and is forced to follow the path on the aluminum or copper wires.

Let Them Move

So what happens if you have separated charges and you connect them with conducting material? Providing a path for charges to move, and making that path out of materials that allow easy movement, results in a flow of charge (electrons) called a current. The electrons will flow from a location that is negative to one that is positive. This can happen quickly and then stop, as with a spark. Or, in the case of a battery connected to a conducting loop (called a circuit. ), it continues to happen until the battery runs out of energy. 

•  If the current goes in one direction all the time, it is called DC, or direct current. 
•  In your home, however, the same charges move back and forth, so this is called AC, or alternating current. 

Force of Charges

Scientists discovered that opposite charges attract, and like charges repel. So positive-positive and negative-negative would repel, while positive-negative would attract. Physicists use the term electric force to describe these attractions and repulsions. The electric forces are much stronger when negative charges are closer to positive charges. The further apart two charges are, the weaker the electric force. Also, the greater the charges, the greater the electric force will be.

ELECTRICITY: SEPARATING CHARGES #2

Separating Charges

Atoms start out with the same number of negative charges (electrons), and positive charges (protons). Under certain conditions, electrons can be removed from, or added to atoms. Removing electrons would leave the atom with more positives than negatives, and we call this a positive ion (An ion is a charged atom). Conversely, adding electrons to an atom would result in a negative ion. If you do this enough times, you can make an object positive or negative.

Friction is one of the ways to separate charge. Have you ever had a science lab where you rub fur on glass rods, or try to make static cling? When you do that rubbing, you are actually rubbing electrons off one object and onto another. When you scuff your feet on the rug, especially in the winter, you can often charge yourself. Clothes tumbling in the dryer often cling together and crackle when you separate them. Lightning is produced, in part, because of air blowing over land. You can also use batteries to separate charge.

Static Charges

Electrons can move more easily in some objects than in others. If you put a charge on things like glass, plastic, rubber, and wood, that charge stays where you put it. We say the charges are static, and we call this static electricity. 

Materials like glass and plastic are called insulators, or nonconductors. Static electricity can happen on a dry winter day when you walk across a carpet. You are actually building up loads of electrons on your skin. Charges don't "want" to stay separated, however. There is always a tendency for charges to return to their original locations, and all that is needed is a pathway for charges (electrons) to use. 

• When you touch a metal doorknob, for example, electrons can jump and give you a shock. Static charges build up on clouds until they can hold no more. At that point, lightning can occur. The study of electricity where the charges are not moving is called electrostatics.

Beware of Conductors!

If you scuff your feet on your living room rug, you pick up extra electrons and have a negative charge. Electrons move moreeasily through certain materials like metal, which scientists call conductors. When you touch a doorknob (or something else made of metal), which has a positive charge with few electrons,the extra electrons want to jump from you to t  the knob.

ELECTRICITY - MOVING ELECTRONS & CHARGES #1 ....

Moving Electrons and Charges

Electricity is related to charges, and both electrons and protons carry a charge. The amount of the charge is the same for each particle, but opposite in sign. 
Electrons carry a negative charge while protons carry positive charge. The objects around us contain billions and billions of atoms, and each atom contains many protons and electrons. 

The protons are located in the center of the atom, concentrated in a small area called the nucleus. 

The electrons are in motion outside of the nucleus in orbitals. 

The protons are basically trapped inside the nucleus and can't escape the nucleus. As a result, it is moving electrons that are primarily responsible for electricity.

There aren't a lot of places that you can see electricity. The most commonly- observed form of electricity is probably lightning. 

•  Lightning is a big spark that occurs when lots of electrons move from one place to another very quickly. 
• There are three basic forms of lightning:
•  cloud to cloud
• cloud to surface
• surface to cloud. 
• All are created when there is an unequal distribution of electrons. You can also see smaller sparks of electricity in science labs that contain Van de Graff generators, and can see even smaller arcs of electrons at home when you scuff your feet and then touch something like a metal doorknob (static electricity). 

Electricity Around You
It's easy to see the uses of electricity around you. In fact, there are charges around your computer, your house, and your city. 

• Electricity is constantly flowing through all of the wires in your town. There is also electricity in your flash light. That kind of electricity created by batteries is called direct current. The other major type is found in the outlets of your house. That household form of electricity is called alternating current.

FIELD DAY

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ELECTRICITY BASICS

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ELECTRICITY - FARADAY

Faraday Basics

Faraday's law of induction is one of the important concepts of electricity. It looks at the way changing magnetic fields can cause current to flow in wires. Basically, it is a formula/concept that describes how potential difference (voltage difference) is created and how much is created. It's a huge concept to understand that the changing of a magnetic field can create voltage.

Faraday's Work

Michael Faraday was an English physicist working in the early 1800's. He worked with another scientist named Sir Humphrey Davy. Faraday's big discovery happened in 1831 when he found that when you change a magnetic field, you can create an electric current. He did a lot of other work with electricity such as making generators and experimenting with electrochemistry and electrolysis.

Faraday's experiments started with magnetic fields that stayed the same. That setup did not induce current. It was only when he started to change the magnetic fields that the current and voltage were induced (created). He discovered that the changes in the magnetic field and the size of the field were related to the amount of current created. Scientists also use the term magnetic flux. Magnetic flux is a value that is the strength of the magnetic field multiplied by the surface area of the device.

Faraday's Law

You're going to have to review your Greek letters when you memorize the real formula. Here are the basics...

E=dB/dt

"E" is the value of voltage induced (the old name for voltage was "ElectroMotive Force", or EMF. That's the "E" in the equation). The change in time for the experiment is "dt". Time is measured in seconds. Last is "dB" which stands for the change in magnetic flux. The magnetic flux is the field lines of the magnetic field. The flux is equal to BA, where B is the magnetic field strength, and A is the area. This formula is a bit harder than those you may have seen before.

In English: the amount of voltage created is equal to the change in magnetic flux divided by the change in time. The bigger the change you have in the magnetic field, the greater amount of voltage.

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ELECTRICITY - HOW TO MEASURE

Learn about Electricity:

Electricity is a very useful form of energy. 

Electricity can be used to perform work such as:

• Heating our homes or our food (electrical energy is converted into light and heat energy)
• Lighting our lamps (electrical energy is converted into light and heat energy)
• Powering our computers (electrical energy is converted into light, heat and sound energy) or
• Powering a motor (electrical energy is converted into movement, heat and sound energy).

 

  

But where do these items get their electricity?

All appliances, whether small or large, need a power source.

What is a power source?

A power source provides a steady flow of electrons. Larger appliances like heaters and large computers usually get their power from the mains. But small batteries (cells) can also be a power source.

The problem with electrical energy obtained from battery power though, is that battery power eventually runs out and the battery has to be thrown away or recharged. On the other hand, electricity flowing from a mains doesn’t run out is much more powerful (and dangerous so be careful!).

Electricity is a “secondary” source of energy. In other words other sources of energy are needed to produce electricity.

 

What is an electrical circuit?

Electrical current needs a PATH on which to travel. Another name for this path is a circuit.  Electricity flows from the power source, in a loop or a circuit, back to the power source. This means that the electricity must start and finish at the same power source. If the circuit is not complete (i.e. if the loop is not closed) then electricity cannot flow through it properly.

Which one of these loops allows electricity to flow?

LOOP1 or LOOP2?  

Explain your answer.

LOOP 1:

LOOP 2:

Electricity flowing through a circuit is called a current.

A load is a device that uses electricity (like a buzzer of a light blub). The load needs electrical energy to be able work.

The electric current from the power source flows from one place to another through the wire of a circuit.

Conductors and Insulators:

 These metal wires (conductors) are often wrapped in plastic (insulators) so as to stop the electric current flowing into objects that touch the wire.

If electricity flows through an object, then scientists say the object conducts electricity, and they call it a conductor. 

Metals are very good conductors. A small bit of energy is released as heat when electricity flows through the conductor.

If electricity doesn’t flow through an object then scientists call it an insulator. Plastic, wood and rubber are all very good insulators.

Here’s an experiment you can do at home to test if different materials are insulators or conductors.

You can increase a circuit by increasing the length of the connecting wire. What do you think will happen to the light bulb as the wire gets longer? How about as the wire gets shorter?

 

What is a switch?

 Switches allow you control over the circuit. You can stop the flow of electricity by breaking the circuit. When the switch is in the “on” position the circuit is complete. When the switch is “off” position the circuit is broken.

Here are some instructions to help you do some science at home and make your own switch.

 

How do I draw a circuit?

Sometimes circuits are drawn using special symbols. These symbols make it faster and easier to draw circuits and once you understand what the different symbols stand for, these diagrams are very easy to understand.  However if you don’t understand what the different symbols stand for, then the diagrams look a little strange!

Here is a chart to help you to understand the different circuit symbols that are used in when drawing the different components of the circuit. Each circuit component has it’s own symbol. These symbols are universal so we call all understand each other’s diagrams.

 

“In Series” or “In Parallel” Circuits:

Whenever two components are joined together in the same circuit, there are two different ways they can be wired: in series or in parallel.

In the in series circuit the components are joined together in one bigger circuit i.e. one continuous loop. 

Electricity passes first through one component first then the next one. 

A disadvantage of the in series circuit is that when one component malfunctions, the other components will stop working.

Another option would be to make two SMALLER circuits with each bulb having it’s OWN circuit parallel to one other. A major advantage of parallel circuits is that if one component malfunctions, the other continues to function.

The diagram below shows the difference between these two types of circuits.

Batteries can also be connected in parallel or in series. But, if you are using more than one battery in a circuit they need to all face in the same direction to work. If two batteries are connected in series, then the voltages add together.

Adding more cells in a line (in series) will make the blub burn brighter.

What do you think would happen if you add too many cells in the series?

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ELECTRICITY - VOCAB TERMS & DEFINITIONS

Ampere - The ampere is the standard unit of measure of electric current. It is sometimes written as amp. 

Alternating current (AC) - An electric current that reverses direction on a periodic basis. It is widely used to transport power on power lines. 

Battery - A device that stores and produces electricity from chemical cells.  A battery has chemicals inside it. The battery is linked to a circuit. Then the chemicals inside the battery react together. This pushes a flow of electrons around the circuit.



Capacitor - A basic electrical component that stores electric charge. Capacitors are made from two electrical conductors separated by an insulator. 

Closed Circuit - circuit in which an electric current can flow from the power source to an object &  back to the power source in an unbroken pathsimple closed circuit

Conductivity - ability of an object to conduct or transmit heat, electricity, or sound


Conductor - material that can allow heat, light, sound, or electricity to pass through it easily.

• Example:  Metal is a good conductor of heat & electricity because it transmits them so easily (A material that allows the free flow of electric charge. Copper wiring is the most widely used electrical conductor.)

Coulomb's law - A law of physics that describes the electrostatic interaction between charged particles. 

Current electricity - the flow of electrons through a continuous path, or loop, from a power source & back to the power source. 

Diode - An electronic component that only allows current flow in one direction. 

Direct current (DC) - A type of current that only flows in one direction (unlike AC which periodically reverses direction). 
Dry cell battery - batteries that use paste-like chemicals to produce electricity

• Example:  used to power watches, toys, remote controls, portable radios, cell phones, calculators, flashlights

• some dry cell batteries can be recharged

Electric charge - This is a basic characteristic of matter that is based on the balance of protons (positive charge) and electrons (negative charge). The standard unit for electric charge is the coulomb. 

Electric circuit - An electric circuit is a collection of electronic components connected by a conductive wire that allows for electric current to flow. 

Electric current - Electric current is the flow of electric charge through a material. The standard unit for electric current is the ampere. 


Electricity - form of energy produced when electrons move, or flow, from one atom to another atom.  There are two types of electricity - static electricity & current electricity.


Electric potential - The electric potential is the difference in electrical charge between two points in a circuit. It is also called the voltage. The standard unit for electric potential is volts. 

Electromagnetism - The interaction between magnetic fields and electric currents. 

Electron - A basic subatomic particle found in all atoms, electrons carry electricity by flowing from one atom to the next in a conductive material. 

Insulator - A material in which electronic charge does not flow freely and does not conduct the flow of electric current, heat, light, or sound.

• Example:  Rubber is a good insulator for both electricity & heatIf one light bulb (or resistor) is turned off or breaks, the current will follow the other path.

Magnetic field - The magnetic influence produced by electric currents and magnetic materials. 

Ohm - The standard unit of measure for resistance. 

Ohm's law - A law of physics that describes the relationship between voltage, current, and resistance using the equation V = IR. 

Open Circuit - circuit in which an electric current cannot flow from the power source to an object & back to the power source
caused by a break in the circuit; switch is turned off & electric current is stopped at the switch                                                                     

Parallel Circuit - electric circuit that has more than one path for the current to follow.

In a parallel circuit, electricity can pass along different paths to power different loads.

Pole - the ends of a battery (positive pole & negative pole) & a magnets (north & south pole). 

Resistance - measure of how much a materiel slows down or stops electricity.  measured in ohms
Example:  Rubber has higher resistance so it is a poor conductor of electricity.  Copper has low resistance so it is a good conductor of electricity.
Calculating Resistance
Use the formula R = V/I

R = resistance (ohms)
V = voltage (volts)
I = current (amps)

Resistor - A basic electronic component that prevents the flow of electric current. 

Semiconductor - A material that behaves between a conductor and an insulator depending on the conditions. Silicon is a widely used semiconductor in electronics. 

Series Circuit - electric circuit that has only one path for the current to follow.  If one light bulb (or resistor) is turned off or breaks, the path is broken & the current will stop.

A series circuit has only one path of electricity. It provides power for more than one electrical load.

Static electricity - The build up of an electric charge on the surface of an object. The charge remains in one area rather than flowing to another area.  Rubbing together two objects made of different materials can produce static electricity.

• Example:  static electricity can be produce when a latex balloon is rubbed on a wool sweater.  Lightning 

Transformer - An electrical component that transfers electrical energy using inductive coupling between two winding circuits. 

Transistor - A semiconductor device used in an electric circuit to regulate current flow to act as a gate, switch, or amplifier for electronic signals. 

Volt - The standard unit of measure for electric potential (voltage). 

Voltage - Voltage is the name for the electric force that causes electrons to flow. It's the measure of potential difference between two points in the circuit. Voltage may come from a battery or a power plant.
Watt - The standard unit of measure used for electric power. 
Wet cell battery - batteries that use liquid chemicals to produce electricity 

• Example:  used in cars, trucks, & large construction equipment to provide power to start engines

They are usually about twice the size of a shoe box.

Wet-cell batteries contain lead and a solution of sulfuric acid.

Conductors and insulators - Conductors are materials that allow electricity to flow easily. Most types of metal are good conductors, which is why we use metal for electrical wire. Copperis a good conductor and isn't too expensive, so it's used a lot for the wiring in homes today. Insulators are the opposite of conductors. An insulator is a material that doesn't carry electricity. Insulators are important because they can protect us from electricity. Materials like rubber, plastic, and paper are good insulators.
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